Profile biphasic

The time profiles of the absorbance due to MV+ at 600 nm are illustrated in Figures 18. Note that they depend on the MV2+ concentration. The curves for the poly(A/St/Phen)-MV2+ systems are biphasic and can be explained in terms of a simple mechanism illustrated in Scheme 2. Here, D A, A represents a compartmentalized Phen moiety (D) and MV2+ dications (A) bound to the hydrophobic microdomain. 

Recently, Brich and coworkers (40) reported the synthesis of lactide/glycolide polymers branched with different polyols. Polyvinyl-alcohol and dextran acetate were used to afford polymers exhibiting degradation profiles significantly different from that of linear poly-lactides. The biphasic release profile often observed with the linear polyesters was smoothened somewhat to a monophasic profile. Further, the overall degradation rate is accelerated. It was speculated that these polymers can potentially afford more uniform drug release kinetics. This potential has not yet been fully demonstrated. 

Because electrode measurements of O2 uptake can detect intra- and extracellular oxidase activity, this assay can be used to measure the respiratory burst elicited by soluble and particulate stimuli. What is somewhat surprising is that, during stimulation of neutrophils with agonists such as fMet-Leu-Phe, the activated O2 uptake profile is biphasic (Fig. 5.11c). A rapid burst of O2 uptake (which coincides with measurements of cytochrome c reduction) is followed by a more sustained activity of lower magnitude. 

The elimination rate of Li+ from the body is variable. It is quite rapid during the first 10 hours after ingestion, and this period accounts for about 40% of the total Li+ excretion. However, the remaining portion of the Li+ dose is excreted very slowly over 14 days. Because of this biphasic elimination rate, clinically useful serum Li+ concentrations are usually determined 12 hours after the last dose. This period assures a relatively accurate reflection of the Li+ concentration, since it is beyond the most variable portion (rapid elimination phase) of the Li+ elimination profile. 

Preliminary in vivo experiments carried out on this biphasic pulsed release device containing ibuprofen as a model drug reveal two distinct peaks in plasma profiles, thus indicating that the in vitro results are in good agreement with the in vivo blood levels. 

Many experimentalists are familiar with this principle of doping a sample with a species that couples better with the microwave irradiation and so can act as a thermal dissipater. What is often less appreciated is the general nature of this process, as not only solid/liquid interfaces but also liquid/liquid biphasic systems such as emulsions show the same effects59-63. Figure 6.2 represents the heating profiles of toluene and a perfluorinated solvent first independently and then as an emulsion. A similar trend can be seen in a hexane/acetonitrile mixture, although because of the superior heating capacity of acetonitrile the effect is less pronounced. 

Concentration profiles showed the mono-telomers to be the primary products, with the exo-2-hydroxy group being more reactive than the more shielded and hydrogen-bonded endo-5-hydroxy group. With continuous addition of butadiene, a final yield of 60% di-telomer was obtained after 24 h. If the reaction was run with 5 eq. of butadiene loaded in the reactor, but without base, mono-telomer selectivity was 97% after 2 h at 68% conversion. Addition of an NaOH solution resulted in complete conversion of isosorbide, accompanied by a large increase in di-telomer formation (up to 60%). Isomannide and isoidide gave almost exclusively the mono-telomer under aqueous biphasic conditions at more or less the same conversion levels (around 60%). Competitive reactions between isomannide and isoidide in DMSO and water showed improved reactivity of the exo-hydroxy group in aqueous media. 

Kmi would be the standard Michaelis constant for the binding of the first substrate, if [ESS] = 0. Km2 would be the standard Michaelis constant for the binding of the second substrate, if [E] = 0 (i.e., the first binding site is saturated). In the complete equation, these constants are not true Km values, but their form (i.e., Km] = (k2 + k25)/k 2) and significance are analogous. Likewise, k25 and k35 are Vmi/Et and Vm2/Et terms when the enzyme is saturated with one and two substrate molecules, respectively. Equation (10) describes several non-Michaelis-Menten kinetic profiles. Autoactivation (sigmoidal saturation curve) occurs when k35 > k24 or Km2 < Km 1, substrate inhibition occurs when k24 > 35, and a biphasic saturation... 

A second type of nonhyperbolic saturation kinetics became apparent during studies on the metabolism of naproxen to desmethylnaproxen (32). Studies with human liver microsomes showed that naproxen metabolism has biphasic kinetics and is activated by dapsone (T. Tracy, unpublished results). The unactivated data shows what appears to be a typical concentration profile for metabolism by at least two different enzymes. However, a similar biphasic profile was obtained with expressed enzyme (25). This biphasic kinetic profile is observed with the two-substrate model when V/rn2 > Eml and Kml Km2. The appropriate equation for the two-site model when [S] < Kml is... 

From Equation (5.139), called the Michaelis-Menten equation, one sees that the rate of formation of P is proportional to the concentration of A at low concentrations (i.e., first-order) and independent of the concentration of A at high concentrations (i.e., zero-order). The general biphasic kinetic profile is shown in Figure 5.21. Usually, experimental runs are carried out in such a way that the concentration of A is very high compared to that of [E]0. All of the enzyme is bound to the substrate and the reaction takes place at a maximum velocity. Then Equation (5.139) becomes ... 

Figure 8.4 shows the influence of e on the x (r) shape. For fixed (k, A), we simulated the time courses for e = 0.5, 1, 2, 5. It is noted that the shape of the substrate profiles varies remarkably with the values of e thus profiles of biphasic, power-law, and nonlinear type are observed. So, the sensitivity of the kinetic profile regarding the available substrate and enzyme amounts is studied by using several e values for low substrate or high enzyme amounts the process behaves according to two decaying convex phases, in the reverse situation the kinetic profile is concave, revealing nonlinear behavior. 

Immunoglobulin profiles of human cervical mucus indicate approximately twice as much IgG (30mg/dl) as IgA (15mg/dl) overall however, there are both biphasic and menstrual cycle influences on Ig levels [169], Different from blood plasma, the IgA2 subclass predominates in female genital tract secretions with lesser amounts of IgGAl [170],... 

The terminal elimination half-life was 20 % lower in patients compared to healthy subjects. Probably the elimination half-life was not accurately determined in patients as XYZ456 concentrations were close to the lower limit of quantification. Thus, as the elimination has a biphasic profile, for patients this elimination half-life probably corresponds to a mix of ti/2,xi and ti/2,xz. 

SA in Table II - nmoles/hr/mg protein and N.D - not detectable. Tobacco, soy cultures and barley seedlings were the best source of ALS, both in terms of specific activity and total units. The enzyme preparations from all sources were unstable in buffer solutions in spite of protective thiol agents. The inactivation of ALS in the crude extract of tobacco showed a distinct biphasic kinetics, implying the presence of at least two isozymes (unpublished observations). The presence of two ALS genes in tobacco (29) and at least three in microorganisms (18) has also been noted by other workers. ALS from barley was most amenable to purification. Table III gives a profile for the rapid purification of this enzyme with high recovery. 

Misra, A., et al. (1997), Biphasic testosterone delivery profile observed with two different transdermal formulations, Pharm. Res., 14(9), 1264-1268. 

The two sites also differ in their pH stability towards iron release. Experiments on serum transferrin showed that one site loses iron at a pH near 6.0, and the other at a pH nearer 5.0 (203, 204), giving a distinctly biphasic pH-induced release profile (Fig. 28). The acid-stable A site was later shown to be the C-terminal site (202). It is this differential response to pH, together with kinetic effects (below), that enables N-terminal and C-terminal monoferric transferrins to be prepared (200). Although the N-terminal site is more labile, both kinetically and to acid, the reasons are not necessarily the same the acid stability may depend on the protonation of specific residues (Section V.B) and is likely to differ somewhat from one transferrin to another in response to sequence changes. The biphasic acid-induced release of iron seen for transferrin is not shared by lactoferrin. Although biphasic release from lactoferrin, in the presence at EDTA, has been reported (205), under most conditions both sites release iron essentially together at a pH(2.5-4.0) several units lower than that for transferrin (Fig. 28). 

Figure 26. (a, b) Transient differential absorption spectra recorded after excitation of Cu.20 in DMF with a 0.5-ps laser pulse at 586 ntn delay times are given on the traces, (c) Growth of the transient absorbance at 660 nm attributed to the charge-transfer state, (d) Decay profile recorded for the above experiment at 660 nm. Note its clear biphasic nature. 

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